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TDA7406T

2.5 Volume Control

2.5.1 Gain/Attenuation Control

The volume control can range from a gain of 32dB up to an attenuation of 79dB; however it is not recommended

to use a gain higher than 20dB for performance reasons.

2.5.2 Soft Step Volume

When the speaker-level is changed, audible clicks could appear at the output. The root cause of those clicks

could either be a DC offset before the speaker-stage or the sudden change of the envelope of the audio signal.

With the SoftStep-feature both kinds of clicks could be reduced to a minimum and are no more audible. The

blend-time from one step to the next is programmable with four different values: 320

µs, 1.28ms, 5.12ms and

20.4ms.

Figure 6. SoftStep-Timing for Volume

Note: For steps more than 0.5dB (Volume) or 1dB (Speaker) the SoftStep mode should be deactivated because it could generate a hard 1dB

step during blending.

2.6 The Seven Band Equalizer

2.6.1 Equalizer Filter

Each filter is realized as a switched capacitor with a 2nd order frequency response.

There are three parameters programmable in the equalizer filter:

s

Attenuation: ±15dB in 1db step resolution (Figure 7 shows the boost and cut response as a function

of frequency at a center frequency of 1kHz.)

s

Center Frequency: This parameter is programmable in the filter stages 1(62/100Hz), 6(4/6.34kHz) and

7(15/16kHz). The others bands are fixed at: 157, 396, 1K and 2.5K Hertz (see Figure 8).

s

Quality Factors: The four possible quality factors are 1, 1.4, 1.8 and 2.2 (see Figure 9).

The center frequency, Q, DC-mode and boost/cut can be set fully independently for each filter. Figure 10 shows

the superposition of all equalizer filter curves for different quality factors.

1dB

0.5dB

-0.5dB

-1dB

SS Time